Of course an average player can fluke like that–there’s nothing incompatible about being average or even shit and having some incredible moments, look at Andy Carroll or even Denilson who scored some crackers from range–especially if he is leading the line for Arsenal for 4 years. What’s more, a mediocre or worse player can fluke like that, which is what Giroud is.
He’s a player who is a negative in terms of defending and pressing/counter-pressing (Oh, but his defensive headers! And him being an outlet when you’re sat deep!!), an extreme negative in terms of his movement when attacking, an extreme negative in terms of his porous link-up play/passing/lack of skill with the ball, who does one thing: score at unimpressive rates for an Arsenal striker.
There is literally zero argument to be made that he’s been anything more than mediocre in his 4 years and change for Arsenal, which is frankly a generous use of wordage.